fix(claude): map WebSearch to Responses web_search

Translate Claude Code web_search_YYYYMMDD server tools to the native OpenAI Responses web_search tool and preserve filters/location. Convert forced Claude tool_choice for web_search to the native Responses tool choice while leaving ordinary custom functions unchanged.

Closes #2936

open-sse/translator/request/claude-to-openai.ts

@@ -27,6 +27,41 @@ function normalizeOpenAIReasoningEffort(effort: unknown): string | undefined {
   return normalized || undefined;
 }
 
+function isClaudeServerWebSearchTool(tool: unknown): tool is JsonRecord {
+  if (!tool || typeof tool !== "object" || Array.isArray(tool)) return false;
+  const record = tool as JsonRecord;
+  return (
+    record.name === "web_search" &&
+    typeof record.type === "string" &&
+    /^web_search_\d{8}$/.test(record.type)
+  );
+}
+
+function toStringArray(value: unknown): string[] {
+  if (!Array.isArray(value)) return [];
+  return value.map((entry) => String(entry || "").trim()).filter(Boolean);
+}
+
+function convertClaudeServerWebSearchTool(tool: JsonRecord): JsonRecord {
+  const allowedDomains = toStringArray(tool.allowed_domains);
+  const blockedDomains = toStringArray(tool.blocked_domains);
+  const filters: JsonRecord = {};
+  if (allowedDomains.length > 0) filters.allowed_domains = allowedDomains;
+  if (blockedDomains.length > 0) filters.blocked_domains = blockedDomains;
+
+  return {
+    type: "web_search",
+    ...(Object.keys(filters).length > 0 ? { filters } : {}),
+    ...(tool.user_location && typeof tool.user_location === "object" && !Array.isArray(tool.user_location)
+      ? { user_location: tool.user_location }
+      : {}),
+  };
+}
+
+function hasClaudeServerWebSearchTool(tools: unknown): boolean {
+  return Array.isArray(tools) && tools.some((tool) => isClaudeServerWebSearchTool(tool));
+}
+
 // Convert Claude request to OpenAI format
 export function claudeToOpenAIRequest(model, body, stream) {
   const result: {
@@ -93,6 +128,10 @@ export function claudeToOpenAIRequest(model, body, stream) {
   if (body.tools && Array.isArray(body.tools)) {
     const normalizedTools = body.tools
       .map((tool) => {
+        if (isClaudeServerWebSearchTool(tool)) {
+          return convertClaudeServerWebSearchTool(tool);
+        }
+
         const name = typeof tool.name === "string" ? tool.name.trim() : "";
         if (!name) return null; // skip tools with empty/invalid name
 
@@ -105,14 +144,7 @@ export function claudeToOpenAIRequest(model, body, stream) {
           },
         };
       })
-      .filter(
-        (
-          tool
-        ): tool is {
-          type: "function";
-          function: { name: string; description: string; parameters: unknown };
-        } => Boolean(tool)
-      );
+      .filter((tool): tool is JsonRecord => Boolean(tool));
 
     if (normalizedTools.length > 0) {
       result.tools = normalizedTools;
@@ -121,7 +153,10 @@ export function claudeToOpenAIRequest(model, body, stream) {
 
   // Tool choice
   if (body.tool_choice) {
-    result.tool_choice = convertToolChoice(body.tool_choice);
+    result.tool_choice = convertToolChoice(
+      body.tool_choice,
+      hasClaudeServerWebSearchTool(body.tools)
+    );
   }
 
   // Reasoning effort: map Claude-side thinking controls to OpenAI reasoning_effort.
@@ -320,7 +355,7 @@ function convertClaudeMessage(msg) {
 }
 
 // Convert tool choice
-function convertToolChoice(choice) {
+function convertToolChoice(choice, hasServerWebSearch = false) {
   if (!choice) return "auto";
   if (typeof choice === "string") return choice;
 
@@ -330,6 +365,9 @@ function convertToolChoice(choice) {
     case TOOL_CHOICE_ANY:
       return "required";
     case "tool":
+      if (hasServerWebSearch && choice.name === "web_search") {
+        return { type: "web_search" };
+      }
       return { type: "function", function: { name: choice.name } };
     default:
       return "auto";

tests/unit/translator-claude-to-openai.test.ts

@@ -52,6 +52,73 @@ test("Claude -> OpenAI maps system blocks, parameters, tool declarations and too
   });
 });
 
+
+
+test("Claude -> OpenAI maps Claude server WebSearch to native Responses web_search", () => {
+  const result = claudeToOpenAIRequest(
+    "gpt-5.5",
+    {
+      messages: [{ role: "user", content: "Search docs" }],
+      tools: [
+        {
+          type: "web_search_20250305",
+          name: "web_search",
+          allowed_domains: ["docs.anthropic.com", ""],
+          blocked_domains: ["spam.example"],
+          max_uses: 8,
+          user_location: { type: "approximate", country: "US" },
+        },
+      ],
+      tool_choice: { type: "tool", name: "web_search" },
+    },
+    true
+  );
+
+  assert.deepEqual(result.tools, [
+    {
+      type: "web_search",
+      filters: {
+        allowed_domains: ["docs.anthropic.com"],
+        blocked_domains: ["spam.example"],
+      },
+      user_location: { type: "approximate", country: "US" },
+    },
+  ]);
+  assert.deepEqual(result.tool_choice, { type: "web_search" });
+});
+
+test("Claude -> OpenAI leaves ordinary web_search function tools as functions", () => {
+  const result = claudeToOpenAIRequest(
+    "gpt-4o",
+    {
+      messages: [{ role: "user", content: "Search docs" }],
+      tools: [
+        {
+          type: "custom",
+          name: "web_search",
+          description: "User-defined search function",
+          input_schema: { type: "object", properties: { query: { type: "string" } } },
+        },
+      ],
+      tool_choice: { type: "tool", name: "web_search" },
+    },
+    false
+  );
+
+  assert.deepEqual(result.tools[0], {
+    type: "function",
+    function: {
+      name: "web_search",
+      description: "User-defined search function",
+      parameters: { type: "object", properties: { query: { type: "string" } } },
+    },
+  });
+  assert.deepEqual(result.tool_choice, {
+    type: "function",
+    function: { name: "web_search" },
+  });
+});
+
 test("Claude -> OpenAI converts assistant text and both base64 and URL images", () => {
   const result = claudeToOpenAIRequest(
     "gpt-4o",